Ho Trung Thong, and

ABSTRACT: In recent Vietnam, integration of agriculture is making advances and usage of pesticides per unit area is rapidly increasing. It may cause environmental problems by pesticides. In our previous study, in three Huong Phong, Huong Van, and Huong Chu communes near Hue city at the central Vietnam, interviews with farmers and the pesticide residue analysis of soils have been conducted to evaluate the risks of pesticides in the environment of Vietnam. Based on the interviews, it was found that the farmers usually misused and overused pesticides. However detected pesticides from soil samples were not higher than the maximum residue limits set by the government. In the target area, soils were sandy, and the sandy soils have weak adsorption power of pesticides. In this condition, pesticides may easily flow into water streams like canals and be concentrated inside the bodies of aquatic organisms like shellfishes. In this study, we focused on Huong Chu commune as the shellfish sampling area because preliminary results for shellfishes taken from a canal of this commune showed higher concentration of pesticides than the soil samples of the same area. For selecting sampling sites of shellfishes and soils, the satellite image with high resolution was used. The digital elevation model (DEM) was produced from Shuttle Radar Topography Mission (90 m mesh) data interpolating by Kriging method and it was overlaid on the near-infrared satellite image. The drainage direction matrix was also calculated from DEM. It was clarified that satellite image and DEM were efficient for the grasp of geographical features, and detection of canals and land altitude of the target area. Thus, the obtained information wa